if you want that XR drive to last more than about 5 minutes you're going to have to be easy on it getting on a plane.

i have about 650 hp in my heat w/ a whippled 502 and mine hops right up on plan w/ a labbed merc 30 at about 2500-3000 rpm.

the additional amount of torque the whipple adds makes a huge difference getting on plane but it's evil on drives if you're not careful :)

I run a 32 on my 25' & I ain't gonna lie, it will loose any drag race. Even if you could "hit it", it would do 1 of 2 things. Either your XR would end up as shipwreck on the bottom of the lake, or you would sit & spin. I have ton's of peeling out with the big prop. I take a 28 with me if there's gonna be water sports involved.
Planing will be a 3 step process. 1/3 throttle, 1/2 throttle & back to 1/3 throttle when it finally grabs.